A Few Watts of Continuous Terahertz Lasers Can Enable Room-temperature Superconductors

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Diamond anvils can make superconductors at or near room temperature in the lab. Now a path to useful room-temperature superconductors has been briefly shown using 10 THz lasers. A few watts of Continuous 10 Thz lasers hitting K3C60 (a fullerene), can make the material behave as a room temperature superconductor. What still must be done is make the 10THz lasers continuous or have 100 million or a billion pulses per second. This seems like a doable way to make useful room temperature superconductors.

An organic material in a metastable phase behaves a little like a room-temperature superconductor when excited with laser light. The behavior fades almost as quickly as the laser pulse that induces it, the team behind the discovery say that with the right light source, it might be possible to keep the material in its superconducting-like state continuously.

IF new pulses could delivered before the sample returns to its non-superconducting equilibrium state, it may be possible to sustain the superconducting-like state continuously.

IF we reach regime where laser source are driving superconductors with continuous wave sources to obtain steady state room temperature operation. This driving this effect in steady state could only need a few watts of power. There is a shortage of continuous-wave light sources available at 10 THz.

The extreme efficiency improvement due to resonant enhancement, nearing two orders of magnitude, is expected to also dramatically reduce unwanted dissipation. This, taken in conjunction with the observed nanosecond-long lifetime, suggests that excitation of the sample with a train of pulses of only 400 μJ cm−2 delivered at a 100 MHz repetition rate—as determined by the inverse lifetime of this state—may yield continuous wave operation. Because this effect is documented here to persist up to room temperature, continuous wave operation would likely have important practical implications. To make this regime experimentally accessible, single-order-of-magnitude improvements in the efficiency of the process or the light–matter coupling strength, combined with suitable developments in high-repetition-rate terahertz sources, would be required.

Shining light at terahertz and mid-infrared frequencies on certain materials is a good way to manipulate their properties. In some cases, this method can even be used to create non-equilibrium material phases that have no analogue under normal conditions.

Described in Nature Physics, Cavalleri and colleagues showed that photoexciting the material with a light source tuned to 10 THz is much more efficient at producing the effect in K3C60 than previous techniques. Indeed, the researchers found they could generate the same superconducting state as in earlier studies with a 100-fold lower laser fluence. This non-equilibrium superconducting state lasts for nanoseconds and appears at room temperature, making the discovery “especially significant”, Cavalleri says.

Nature Physics – Resonant enhancement of photo-induced superconductivity in K3C60

Abstract
Photo-excitation at terahertz and mid-infrared frequencies has emerged as an effective way to manipulate functionalities in quantum materials, in some cases creating non-equilibrium phases that have no equilibrium analogue. In K3C60, a metastable zero-resistance phase was observed that has optical properties, nonlinear electrical transport and pressure dependencies compatible with non-equilibrium high-temperature superconductivity. Here we demonstrate a two-orders-of-magnitude increase in photo-susceptibility near 10 THz excitation frequency. At these drive frequencies, a metastable superconducting-like phase is observed up to room temperature. The discovery of a dominant frequency scale sheds light on the microscopic mechanism underlying photo-induced superconductivity. It also indicates a path towards steady-state operation, limited at present by the availability of a suitable high-repetition-rate optical source at these frequencies.

The search for new non-equilibrium functional phases in quantum materials, such as optically induced ferroelectricity magnetism charge density wave order non-trivial topology and superconductivity has become a central research theme in condensed-matter physics. In the case of K3C60, mid-infrared optical pulses have been extensively documented to yield an unconventional non-equilibrium phase that exhibits metastable zero resistance, extraordinarily high mobility and a superconducting-like gap in the optical conductivity that reduce with applied pressure13, and nonlinear current–voltage characteristics. All these observations are indicative of non-equilibrium high-temperature superconductivity, observed at base temperatures far exceeding the highest equilibrium superconducting critical temperature of any alkali-doped fulleride.